Close a connection if PQexec returned NULL

This happens for Socket connections, not for TCP ones, where a result
containing an error is returned and correctly handled by pq_raise()

Closes ticket #196 but not #192: poll() still doesn't change the
connection closed.

NEWS

@@ -27,6 +27,8 @@ What's new in psycopg 2.5.3
   (:ticket:`#203`).
 - Don't segfault using poorly defined cursor subclasses which forgot to call
   the superclass init (:ticket:`#195`).
+- Mark the connection closed when a Socket connection is broken, as it
+  happens for TCP connections instead (:ticket:`#196`).
 - Fixed possible segfault in named cursors creation.
 - It is now possible to call `get_transaction_status()` on closed connections.
 - Fixed debug build on Windows, thanks to James Emerton.

psycopg/pqpath.c

@@ -417,11 +417,19 @@ pq_complete_error(connectionObject *conn, PGresult **pgres, char **error)
         pq_raise(conn, NULL, pgres);
         /* now *pgres is null */
     }
-    else if (*error != NULL) {
+    else {
+        if (*error != NULL) {
             PyErr_SetString(OperationalError, *error);
         } else {
             PyErr_SetString(OperationalError, "unknown error");
         }
+        /* Trivia: with a broken socket connection PQexec returns NULL, so we
+         * end up here. With a TCP connection we get a pgres with an error
+         * instead, and the connection gets closed in the pq_raise call above
+         * (see ticket #196)
+         */
+        conn->closed = 2;
+    }
 
     if (*error) {
         free(*error);